1. Field of the Invention
The present invention relates to an industrial diamond thin film coating and a method of manufacturing the same.
2. Description of the Prior Art
The life time of machine tools such as cutting tools and grinding tools or other instruments having very hard surfaces or abrasive edges can be prolonged by coating, directly on the hard surfaces or abrasive edges, protection films made of very hard materials such as diamond, titanium carbide, titanium nitride, carbonated titanium nitride, aluminum oxide. Particularly, diamond coating has been believed to be very effective in the cases of coating on surfaces made of nonferrous metals or ceramics.
Such coatings have been formed on surfaces of the tools typically by thermal CVD (chemical vapor deposition) in an apparatus as illustrated in FIG. 1. The apparatus comprises a vacuum chamber 31, a tungsten filament 33 and a holder 35. After mounting an object 34 on the holder 35, a large electric current is caused to pass the filament 33 in order to emit thermal electrons at 1500.degree. C. to 1300.degree. C. A reactive gas comprising carbon is introduced into the chamber from an inlet port 32 at the same time. By virtue of the thermal electrons, the reactive gas is decomposed to coat the object 34 with a diamond film. During coating, the temperature of the object 34 is kept at 400.degree. C. to 1300.degree. C. and the pressure in the chamber at 1 Torr to 350 Torr.
One of the practical problems of these technique is the coming-off or rubbing-off of the diamond film from the surface of a tool. Until now, there has not been yet accomplished sufficient adhesivity of diamond coatings to the surfaces of tools. The difference in thermal expansion coefficient between the diamond film and the underlying surfaces has been considered as a cause of separation of the diamond films from the surface.
Furthermore, it is another shortcoming of the prior art technique that diamond coating is deposited only on such small areas as about .PHI. 2 cm so that the diamond films become very expensive. Still further, because of undesirable disparity in film quality over one surface, the applications in practice have been substantially limited.